Subspace force field

Three modified armbands in use, worn on one's left arm

An emergency transporter armband was a device used by Starfleet personnel during an away team mission to remotely activate the transporters of a starship or runabout for an immediate beam-up in the event of a dangerous situation where verbal communication was not possible, preventing a request for transport in normal circumstances. The armband comprised a type-7 phase discriminator and a subspace emitter. (TNG: "The Best of Both Worlds")

Geordi La Forge modified several transporter armbands in late 2369 to produce a subspace isolation field to protect the crew aboard the runabout from the effects of a temporal fragment. (TNG: "Timescape")